1. Field of the Invention
This invention relates to air deflection systems and, more particularly, to air deflection systems used to control air movement at the underside region of vehicles.
2. Background Art
Ground transportation industries are becoming increasingly concerned about maximizing fuel efficiency for their vehicles. Rising fuel costs and diminishing profit margins have motivated particularly the trucking industry to seek alternative, fuel-efficient designs, particularly for semi-trailers. Environmental concerns focused on emissions and anticipated future government fuel efficiency regulations have also been instrumental in motivating such redesigns.
Given the relatively generic configuration of semi-trailers, and the large number of such vehicles already in use, the industry has focused heavily on retrofitting such vehicles with air deflection systems that will improve their aerodynamic properties. For decades, semi-trailers have incorporated convex deflectors to bridge the region between the upper surface of the towing unit and the front wall of the trailer extending above the towing unit. In the absence of this structure, the trailer presents a flat, forwardly facing wall surface that is in a plane generally perpendicular to the travel direction. As a result, in the absence of some air deflection structure, this trailer region produces a significant amount of drag that accounts for an appreciable loss of fuel efficiency.
Another region of such vehicles that accounts for poor aerodynamic properties is at the trailer sides between the rear wheel assembly and the wheel assembly on the towing vehicle. In the absence of some type of air deflection structure, air tends to be drawn by vacuum into the space beneath the cargo container. This air diversion prevents the maintenance of a laminar air flow along the full lengthwise extent of the trailer. The diverted air pattern also acts against the rear wheel assembly, the underside of the cargo container, and other components, that results in additional, unwanted drag. Typically, none of these components at the underside of the cargo container is designed with aerodynamic properties as a focus.
It is known to incorporate air deflection systems, in the form of side skirts, on semi-trailers. While the incorporation of these side skirts is desired, their use is practical only if they can be installed and maintained in an economically feasible manner.
If the process for installing the skirts is time consuming and difficult, operators may opt to leave these structures off. Inherently, these structures are installed with a relatively high degree of difficulty by reason of their size. If each side is installed as a single lengthwise unit, several individuals may be required to support the same and work together to secure it to the trailer. While construction of each side skirt with multiple joinable pieces may obviate this problem, it introduces other problems by requiring potentially more complicated structures and more complicated assembly steps as the individual components are joined together.
Side skirts must also be positively held in place. The release of part or all of the skirt structure during vehicle operation could endanger individuals in the vicinity of the semi-trailer or other vehicle operators.
At the same time, these skirt assemblies must have the ability to withstand potentially high wind loading and absorb impacts from road hazards, other vehicles, or any other encountered object. To effectively control air flow, the skirts must depend from the bottom of the cargo container into relatively close proximity to the ground. This makes the skirts prone to intercepting foreign objects that commonly find their way onto roadways. As a result, some level of flexibility and resistance to breakage must be incorporated into these designs.
It is known to construct the skirt assemblies with joined upper and lower components, with the former being more rigid for mounting and latter more flexible to deform without breaking under anticipated impacts. In the absence of some accommodation for this condition, part or all of the side skirt may break loose, again thereby posing a danger to those in the vicinity of the vehicle.
From the onset, use of side skirt assemblies is a realistic possibility only if they can be made relatively economically while remaining intact without a significant investment in maintenance or concern about failure. If the original design is relatively expensive, one must weigh the advantages of using a side skirt assembly versus operating the vehicle with less than desired aerodynamic properties.
The industry continues to seek out such side skirt assemblies that can be purchased and maintained economically, are capable of being installed without a high level of difficulty or expense, effectively divert air flow, and are not prone to failing under normal operating conditions.